A plug-in coupler for gas insulated high-voltage electric distribution cells comprises an outer insulating body made of resin housing therein metal contacts or connectors for electrical connection to a high-voltage cell (for example through a T-shaped connector coupled to the cell). Generally the cells are three phase cells, therefore they comprise three T-shaped connectors and three couplers, one for each phase. The coupler is designed to enable injecting signals between 2 and 40 Mhz into a high-voltage conductor. The device must achieve two functions, having an impedance to the high frequency signals of very low value to enable coupling them to the high-voltage conductor and a very high impedance at 50 Hz, thus being able to assure the insulation level of the device taking into account that it is connected to high voltage.
The coupler therefore comprises one or several ceramic condensers having a high impedance at 50 Hz and low impedance at frequencies of the order of Mhz.
The coupler, as can be seen in FIG. 2 is frustoconical shaped (according to DIN C standard) and incorporates a low-voltage circuit for tuning the equipment to the impedances of the line and obtaining a maximum performance in high frequency signal transmission. This circuit is made up of a coil and an impedance adaptation transformer (FIG. 1, reference 20).
Sometimes it is also necessary to accurately measure the line voltage, for which the coupling device should house a voltage divider therein. The condenser needed to perform the mentioned function of the coupler is large and virtually occupies the entire central part of the coupling device, such that the voltage divider would have to occupy the space left by the condenser at the connection end (narrower end), but this entails a problem because the connection end is at high-voltage, whereas the voltage is zero at the other end (wider end). The voltage divider also has to have an end connected to the high-voltage and the other to zero voltage, but if one attempts to place it in the end left by the condenser, the end at zero voltage of the divider is in the same area as the end at high-voltage of the condenser, which involves a poor distribution of the electric field and the insulation of the device.